1. Field of the Invention
The present general inventive concept relates to a method and apparatus encode and/or decode audio signals or video signals, and more particularly, to a method and apparatus to scalably encode and/or decode audio signals or video signals.
2. Description of the Related Art
An audio signal or a video signal can be encoded into a plurality of layers by controlling a bit rate by providing scalability. When a network becomes overloaded because of the encoding of an audio signal or a video signal into a plurality of layers, when a decoder cannot perform decoding, or when a bit rate is decreased according to a user's setting, the sound or image quality decreases, but the original signal can be restored by using only a part of a bitstream that corresponds to some of the layers.
Examples of important factors for providing scalability include transformation, quantization, bit-plane coding, data reordering, etc. Because of a tradeoff relationship between coding efficiency and the sound or image quality, when the coding efficiency is increased, the sound or image quality is decreased. On the other hand, when the coding efficiency is decreased, the sound or image quality is increased. In order to increase coding efficiency, an overhead caused by scalability should be small. In order to increase the sound or image quality, transformation, quantization, data reordering, etc. should be optimized. Therefore, the coding efficiency and the sound or image quality have opposite characteristics, and accordingly encoding that appropriately satisfies both the coding efficiency and the sound or image quality is needed.
In a codec that provides scalability on the basis of bit-plane coding and data reordering, the number of calculations to be executed is decreased but the quality of sound at low layers rapidly decreases. More specifically, when bit-plane coding is applied, quantization noise is increased by undecoded symbols. In addition, due to a lack of bits to be transmitted in low layers, a bandwidth that can be restored is decreased as layers become lower, and a muffled sound is generated. Therefore, the sound quality at low layers rapidly decreases.